Radio receiving apparatus, radio transmission apparatus, and communication method

ABSTRACT

Provided are a radio transmission apparatus, a radio receiving apparatus, a radio communication system, and a communication method that make it possible for the radio transmission apparatus performing OFDMA transmission to highly efficiently determine a radio receiving apparatus that is caused to participate in the OFDMA transmission. The radio transmission apparatus that performs OFDMA transmission with a plurality of radio receiving apparatuses includes a reception unit that has a function of performing carrier sense and a function of receiving a function information response frame including function response information indicating that a function of performing the OFDMA transmission is included, and a transmission unit that has a function of switching whether or not to transmit a frame to at least one of the plurality of radio receiving apparatuses on a basis of the carrier sense.

TECHNICAL FIELD

The present invention relates to a radio receiving apparatus, a radiotransmission apparatus, and a communication method.

BACKGROUND ART

As an advanced standard of IEEE802.11n which is a radio LAN (Local areanetwork) standard that has been widely put into use, the IEEE802.11acstandard has been developed by the IEEE (The Institute of Electrical andElectronics Engineers, Inc.). Currently, standardization efforts forIEEE802.11ax are conducted as a successive standard of IEEE802.11n/ac.In the current radio LAN system, interference due to an increase in thenumber of terminals per unit area is becoming a large problem, and sucha congested environment needs to be considered in an IEEE802.11axstandard. On the other hand, differently from the previous radio LANstandards, not only improvement of peak throughput but also improvementof user throughput are cited as main required conditions in theIEEE802.11ax standard. It is essential to introduce a highly efficientsimultaneous multiplexing transmission scheme (access scheme) in orderto improve the user throughput.

In standards before the IEEE802.11n standard, an access scheme of anautonomous distributed control type called CSMA/CA (Carrier sensemultiple access with collision avoidance) has been adopted as the accessscheme. In IEEE802.11ac, space division multiple access (SDMA) by amulti-user multiple-input multiple-output (MU-MIMO) technique is newlyadded.

The IEEE802.11ax standard is required to further improve the accessscheme for improving the user throughput. As the highly efficient accessscheme, there is Orthogonal Frequency Division Multiple Access (OFDMA).The OFDMA is a scheme for, by using characteristics of OrthogonalFrequency Division Multiplexing (OFDM) which allows enhancement offrequency efficiency by arranging a large number of orthogonalsub-carriers densely at intervals of a reciprocal of a signal duration,allocating any number of sub-carriers (or a frequency band composed of agroup of contiguous sub-carriers) with good characteristics to each ofradio receiving apparatuses in accordance with reception characteristicsdifferent in each of radio receiving apparatuses in a multipathenvironment, and thereby further increasing substantial frequencyefficiency. It is expected that the user throughput is improved byintroducing the OFDMA to the IEEE802.11ax standard (NPL 1).

In order for a radio transmission apparatus to arrange a data signaladdressed to each of radio receiving apparatuses in a suitablesub-carrier, the radio transmission apparatus needs to acquire receptioncharacteristics between the radio transmission apparatus and the radioreceiving apparatus with high accuracy. For example, radio measurementprocedures in which a radio transmission apparatus requests a radioreceiving apparatus to measure reception characteristics of the radioreceiving apparatus and report a result of the measurement are specifiedin the IEEE802.11 standard. By performing the radio measurementprocedures with radio receiving apparatuses, the radio transmissionapparatus is able to grasp reception characteristics of the radioreceiving apparatuses. However, the radio measurement procedures need tobe performed in accordance with a mechanism of the CSMA/CA. Thus, in acase where the radio transmission apparatus performs OFDMA transmissionwith a plurality of radio receiving apparatuses, a large amount of radioresources are allocated for the radio measurement procedures, resultingin limitation of improvement of throughput of the OFDMA transmission.

CITATION LIST Non Patent Literature

NPL 1: IEEE 11-13/1395r2, “Simultaneous transmission technologies forHEW”, November 2013.

SUMMARY OF INVENTION Technical Problem

In order for a radio transmission apparatus to arrange a data signaladdressed to each of radio receiving apparatuses in a suitablesub-carrier, the radio transmission apparatus needs to correctly graspreception characteristics of the radio receiving apparatus. In acommunication system which is premised on CSMA/CA, however, a largeamount of radio resources are required to correctly grasp the receptioncharacteristics, so that improvement of throughput of the OFDMAtransmission is limited.

The invention was made in view of such circumstances and an objectthereof is to provide a radio transmission apparatus, a radio receivingapparatus, a radio communication system, and a communication method thatmake it possible for a radio transmission apparatus performing OFDMAtransmission to highly efficiently determine a radio receiving apparatusthat is caused to participate in the OFDMA transmission.

Solution to Problem

A radio transmission apparatus, a radio receiving apparatus, acommunication system, and a communication method according to theinvention for solving the aforementioned problems are as follows.

(1) That is, a radio transmission apparatus of the invention is a radiotransmission apparatus that performs multi-user transmission with aplurality of radio receiving apparatuses, and the radio transmissionapparatus includes a transmission unit that has a function of generatinga function information frame including function information indicatingthat a function of performing the multi-user transmission is includedand that has a function of transmitting the function information frame.

(2) The radio transmission apparatus of the invention is the radiotransmission apparatus according to (1) above that includes a receptionunit that has a function of receiving a function information responseframe which is transmitted by each of the radio receiving apparatusesand which includes function response information indicating that afunction of performing the multi-user transmission is included.

(3) The radio transmission apparatus of the invention is the radiotransmission apparatus according to (2) above, in which a combination ofthe radio receiving apparatuses that are caused to participate in themulti-user transmission is decided on a basis of the function responseinformation.

(4) The radio transmission apparatus of the invention is the radiotransmission apparatus according to (1) above, in which the transmissionunit has a function of transmitting a resource reserving frame and afunction of transmitting a signal frame that includes informationindicating a cyclic shift amount given by the radio receiving apparatusto a resource reserving response frame corresponding to the resourcereserving frame transmitted by the radio receiving apparatus, and theradio transmission apparatus has a reception unit that has a function ofreceiving the resource reserving response frame is included.

(5) A radio receiving apparatus of the invention is a radio receivingapparatus performing communication with a radio transmission apparatusthat performs multi-user transmission with a plurality of radioreceiving apparatuses, and the radio receiving apparatus includes areception unit that has a function of receiving a function informationframe including function information indicating that the radiotransmission apparatus has a function of performing the multi-usertransmission and a transmission unit that has a function of generating afunction information response frame including function responseinformation indicating that the radio receiving apparatus has a functionof participating in the multi-user transmission and that has a functionof transmitting the function information response frame.

(6) The radio receiving apparatus of the invention is the radioreceiving apparatus according to (5) above, in which the reception unithas a function of receiving a resource reserving frame transmitted bythe radio transmission apparatus, and the transmission unit has afunction of generating a resource reserving response frame correspondingto the resource reserving frame and a function of giving a cyclic shiftto the resource reserving response frame.

(7) The radio receiving apparatus of the invention is the radioreceiving apparatus according to (6) above, in which the transmissionunit has a function of transmitting the resource reserving frame to afirst radio resource and a second radio resource, and a cyclic shiftamount of phase shift given to the resource reserving frame transmittedby the first radio resource is different from a cyclic shift amount ofphase shift given to the resource reserving frame transmitted by thesecond radio resource.

(8) The radio receiving apparatus of the invention is the radioreceiving apparatus according to (6) or (7) above, in which the cyclicshift amount of cyclic shift given to the resource reserving responseframe by the transmission unit is signaled by the radio transmissionapparatus.

(9) A communication method of the invention is a communication method ofa radio transmission apparatus that performs multi-user transmissionwith a plurality of radio receiving apparatuses, and the communicationmethod includes the steps of: generating a function information frameincluding function information indicating that a function of performingthe multi-user transmission is included; and transmitting the functioninformation frame.

(10) A communication method of the invention is a communication methodof a radio receiving apparatus performing communication with a radiotransmission apparatus that performs multi-user transmission with aplurality of radio receiving apparatuses, and the communication methodincludes the steps of: receiving a function information frame includingfunction information indicating that the radio transmission apparatushas a function of performing the multi-user transmission; generating afunction information response frame including function responseinformation indicating that the radio receiving apparatus has a functionof participating in the multi-user transmission; and transmitting thefunction information response frame.

(11) A communication system of the invention is a communication systemthat includes a radio transmission apparatus and a plurality of radioreceiving apparatuses, in which the radio transmission apparatus has atransmission unit that has a function of generating a functioninformation frame including function information indicating that afunction of performing the multi-user transmission is included and thathas a function of transmitting the function information frame, and eachof the radio receiving apparatuses has a reception unit that has afunction of receiving the function information frame and a transmissionunit that has a function of generating a function information responseframe including function response information indicating that the radioreceiving apparatus has a function of participating in the multi-usertransmission and that has a function of transmitting the functioninformation response frame.

Advantageous Effects of Invention

According to the invention, since a radio transmission apparatusperforming OFDMA transmission is able to highly efficiently determine aradio receiving apparatus that is caused to participate in the OFDMAtransmission, overhead associated with the OFDMA transmission is able tobe significantly reduced, thus making it possible to greatly improveuser throughput.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a communication system according to theinvention.

FIG. 2 is a schematic block diagram illustrating a configuration exampleof a radio transmission apparatus according to the invention.

FIG. 3 illustrates a configuration example of a frame configuration of asignal of the invention.

FIG. 4 is a flowchart illustrating an example of a communication methodaccording to the invention.

FIG. 5 is a schematic block diagram illustrating a configuration exampleof a radio receiving apparatus according to the invention.

FIG. 6 is a flowchart illustrating an example of a communication methodaccording to the invention.

FIG. 7 illustrates a configuration example of a frame configuration of asignal of the invention.

FIG. 8 illustrates a configuration example of a frame configuration of asignal of the invention.

FIG. 9 illustrates an example of a signal processing output of theinvention.

DESCRIPTION OF EMBODIMENTS 1. First Embodiment

A communication system in the present embodiment includes a radiotransmission apparatus (access point (AP)) and a plurality of radioreceiving apparatuses (stations (STAs)). A network composed of the APand the STAs is called a basic service set (BSS).

The AP and the STAs in the BSS perform communication on the basis ofCSMA/CA (Carrier sense multiple access with collision avoidance). Thoughthe present embodiment is intended for an infrastructure mode in whichthe AP performs communication with a plurality of STAs, a method of thepresent embodiment may be carried out also in an ad hoc mode in whichSTAs directly perform communication with each other.

In an IEEE802.11 system, apparatuses are able to transmit transmissionframes of a plurality of frame types having a common frame format. Thetransmission frames are defined by a physical (PHY) layer, a mediumaccess control (MAC) layer, and a logical link control (LLC) layer.

The transmission frame of the PHY layer is called a physical protocoldata unit (PHY protocol data unit: PPDU). The PPDU is constituted by aphysical layer header (PHY header) including, for example, headerinformation for performing signal processing in the physical layer, aphysical service data unit (PHY service data unit: PSDU) that is a dataunit processed in the physical layer, and the like. The PSDU is able tobe constituted by an aggregated MPDU (A-MPDU) in which a plurality ofMAC protocol data units (MPDUs) each of which serves as a retransmissionunit in a radio section are aggregated.

The PHY header includes reference signals of, for example, a shorttraining field (STF) used for signal detection, synchronization, and thelike and a long training field (LTF) used for acquiring channelinformation for data demodulation, and control signals such as signals(SIGs) in which control information for data demodulation is included.The STF is classified in accordance with a corresponding standard into alegacy-STF (L-STF), a high throughput-STF (HT-STF), a very highthroughput-STF (VHT-STF), and the like, and the LTF and the SIG areclassified similarly into an L-LTF, an HT-LTF and a VHT-LTF, and anL-SIG, an HT-SIG and a VHT-SIG. The VHT-SIG is further classified into aVHT-SIG-A and a VHT-SIG-B.

The PPDU is modulated in accordance with a corresponding standard. Forexample, in the case of an IEEE802.11n standard, the PPDU is modulatedto an orthogonal frequency division multiplexing (OFDM) signal.

The MPDU is constituted by a MAC layer header (MAC header) in which, forexample, header information for performing signal processing in the MAClayer is included, a MAC service data unit (MSDU) that is a data unitprocessed in the MAC layer, or a frame body, and a frame check sequence(FCS) for checking whether or not there is an error in a frame. Aplurality of MSDUs are also able to be aggregated as an aggregated MSDU(A-MSDU).

The frame type of the transmission frame of the MAC layer is roughlyclassified into three data frames of a management frame in which, forexample, a connection state between apparatuses is managed, a controlframe in which a communication state between apparatuses is managed, anda data frame including actual transmission data, and each of the framesis further classified into a plurality of kinds of sub-frame types. Thecontrol frame includes a reception completion notification (Acknowledge:ACK) frame, a transmission request (Request to send: RTS) frame, areception preparation completion (Clear to send: CTS) frame, and thelike. The management frame includes a beacon frame, a probe requestframe, a probe response frame, an authentication frame, a connectionrequest (association request) frame, a connection response (associationresponse) frame, and the like. The data frame includes a data frame, apolling (CF-poll) frame, and the like. Each apparatus is able to grasp aframe type and a sub-frame type of a received frame by reading contentof a frame control field included in a MAC header.

The beacon frame includes an interval (Beacon interval) at which beaconis transmitted and a field in which information (Service set identifier(SSID) or the like) for identifying an AP is described. The AP is ableto periodically broadcast a beacon frame into a BSS and an STA is ableto grasp the AP around the STA by receiving the beacon frame. Graspingof the AP by the STA based on a signal that is broadcasted from the APis referred to as passive scanning. On the other hand, probing of the APby broadcasting a probe request frame into the BSS by the STA isreferred to as active scanning. The AP is able to transmit a proberesponse frame as a response to the probe request frame and descriptioncontent of the probe response frame is equivalent to that of the beaconframe.

The STA recognizes the AP and then performs connection processing forthe AP. The connection processing is classified into an authenticationprocedure and a connection (association) procedure. The STA transmits anauthentication frame to the AP that desires connection. Upon receptionof the authentication frame, the AP transmits, to the STA, anauthentication frame including a status code indicating, for example,whether or not to authenticate the STA. By reading the status codedescribed in the authentication frame, the STA is able to determinewhether or not authentication for the STA is allowed by the AP. Notethat, the AP and the STA are able to exchange an authentication frame aplurality of times.

Subsequently to the authentication procedure, the STA transmits aconnection request frame to the AP to perform the connection procedure.Upon reception of the connection request frame, the AP determineswhether or not to allow connection of the STA and transmits a connectionresponse frame to notify whether or not to allow the connection. Inaddition to the status code indicating whether or not connectionprocessing is allowed, an association identification number (Associationidentifier: AID) for identifying the STA is described in the connectionresponse frame. The AP is able to manage a plurality of STAs by settingdifferent AIDs to the STAs that have been allowed to make connection.

After the connection processing is performed, the AP and the STA performactual data transmission. In the IEEE802.11 system, a distributedcoordination function (DCF), a point coordination function (PCF), anextended function thereof (such as a hybrid coordination function: HCF),and the like are defined. Description will be given below by taking acase where the AP transmits a signal to the STA by the DCF as anexample.

In the DCF, prior to communication, the AP and the STA perform carriersense (CS) for checking a usage state of a radio channel around the APand the STA. For example, in a case where the AP serving as atransmission station receives, by the radio channel, a signal having alevel higher than a clear channel assessment level (CCA level) that isdefined in advance, the AP postpones transmission of a transmissionframe by the radio channel to enter into a reception operation.Hereinafter, in the radio channel, a state in which a signal having alevel equal to or greater than the CCA level is detected is referred toas a busy state and a state in which a signal having a level equal to orgreater than the CCA level is not detected is referred to as an idlestate. The CS performed by each apparatus on the basis of power of anactually received signal in this manner is called physical carrier sense(physical CS). Note that, the CCA level is also referred to as a carriersense level (CS level) or a CCA threshold (CCAT). Note that, whendetecting a signal having a level equal to or greater than the CCAlevel, the AP and the STA enter into an operation of demodulating atleast a signal of the PHY layer.

The AP performs carrier sense during a frame interval (Inter framespace: IFS) according to a type of the transmission frame to betransmitted and determines whether the radio channel is in the busystate or the idle state. A time period in which the AP performs thecarrier sense varies in accordance with a frame type and a sub-frametype of the transmission frame to be transmitted by the AP. In theIEEE802.11 system, a plurality of IFSs having different time periods aredefined, and there are a short frame interval (Short IFS: SIFS) used fora transmission frame to which highest priority is given, a polling frameinterval (PCF IFS: PIFS) used for a transmission frame having relativelyhigh priority, a distributed control frame interval (DCF IFS: DIFS) usedfor a transmission frame having lowest priority, and the like. When theAP transmits a data frame by the DCF, the AP uses the DIFS.

The AP waits for the DIFS and then further waits for a random back-offtime for preventing frame collision. The random back-off time calledcontention window (CW) is used in the IEEE802.11 system. In the CSMA/CA,it is premised that a transmission frame transmitted by a certaintransmission station is received by a reception station in a state wherethere is no interference from other transmission stations. Therefore,when transmission frames are transmitted by transmission stations at thesame timing, the frames collide with each other so that the receptionstation is not able to receive the transmission frames correctly. Thus,when each of the transmission stations waits for a time that is setrandomly before starting the transmission, the frame collision isprevented. When determining that the radio channel is in the idle stateby the carrier sense, the AP starts countdown of the CW, acquires atransmission right only when the CW indicates 0, and is allowed totransmit a data frame to the STA. Note that, in a case where the APdetermines that the radio channel is in the busy state by the carriersense during countdown of the CW, the AP stops countdown of the CW. In acase where the radio channel is brought into the idle state, the APrestarts countdown of the remaining CW subsequently to the previous IFS.

The STA serving as a reception station receives a transmission frame,reads a PHY header of the transmission frame, and demodulates thereceived transmission frame. By reading a MAC header of a demodulatedsignal, the STA is able to recognize whether or not the transmissionframe is addressed to the STA. Note that, the STA is also able todetermine an address of the transmission frame on the basis ofinformation (for example, a group identification number (Groupidentifier: Group ID) described in the VHT-SIG-A) described in the PHYheader.

When the STA determines that the received transmission frame isaddressed to the STA and the transmission frame is demodulated withouterror, the STA needs to transmit, to the AP serving as the transmissionstation, an ACK frame indicating that the frame is able to be receivedcorrectly. The ACK frame is one of transmission frames that aretransmitted only by waiting for the time period of the SIFS (withouttaking the random back-off time) and that have highest priority. Uponreception of the ACK frame transmitted from the STA, the AP ends aseries of communication. Note that, when the STA is not able to receivethe frame correctly, the STA does not transmit the ACK. Thus, when theAP has not received the ACK frame from the reception station for a fixedtime period (length of SIFS+ACK frame) after the frame transmission, itis considered that communication has failed and the communication ends.In this manner, the end of one communication (also referred to as burst)of the IEEE802.11 system is always determined on the basis of whether ornot the ACK frame is received except for special cases such as a casewhere a broadcast signal such as a beacon frame is transmitted and acase where fragmentation for fragment of transmission data is used.

When determining that the received transmission frame is not addressedto the STA, the STA sets a network allocation vector (NAV) on the basisof a length of the transmission frame described in the PHY header or thelike. The STA does not attempt to perform communication during a timeperiod that is set to the NAV. That is, since the STA performs, duringthe time period that is set to the NAV, the same operation as theoperation performed when it is determined that the radio channel is inthe busy state by the physical CS, communication control by the NAV isalso called virtual carrier sense (virtual CS). The NAV is set not onlyon the basis of information described in the PHY header, but also by atransmission request (Request to send: RTS) frame or a receptionpreparation completion (Clear to send: CTS) frame that is introduced tosolve a hidden node problem. The frame of the MAC layer of the RTS frameor the CTS frame includes a receiver address field indicating an addressof the frame and a duration field indicating a time period of the NAV. Aterminal apparatus that transmits the RTS frame or the CTS frame is ableto describe, in the duration field, a time period during which a radioresource is to be occupied. The terminal apparatus that has received theRTS frame sets the NAV by a length described in the duration field in acase where the RTS frame is not addressed to the terminal apparatus. Onthe other hand, in a case where the RTS frame is addressed to theterminal apparatus, when the SIFS has lapsed after the RTS frame hasbeen received, the terminal apparatus that has transmitted the RTS frameuses a value of the duration field described in the RTS frame toestimate a time period during which the radio resource is occupied andtransmits a CTS frame in which the value is written in the durationfield.

While each apparatus performs carrier sense to autonomously acquire atransmission right in the DCF, a control station called a pointcoordinator (PC) controls a transmission right of each apparatus in theBSS in the PCF. The AP generally serves as the PC and acquires atransmission right of the STA in the BSS.

A communication period by the PCF includes a contention free period(CFP) and a contention period (CP). Communication is performed on thebasis of the DCF described above during the CP and the PC controls thetransmission right during the CFP. The AP serving as the PC broadcasts abeacon frame, in which a time period of the CFP (CFP Max duration) orthe like is described, into the BSS before communication by the PCF.Note that, the PIFS is used to transmit the beacon frame that isbroadcasted when transmission of the PCF starts and the beacon frame istransmitted without waiting for the CW. The STA having received thebeacon frame sets the time period of the CFP described in the beaconframe to the NAV. After that, until the NAV has lapsed or a signal (forexample, a data frame including CF-end) by which end of the CFP isbroadcasted into the BSS is received, the STA is able to acquire thetransmission right only when the STA receives a signal (for example, adata frame including CF-poll) that is transmitted by the PC and signalsacquisition of the transmission right. Note that, since collision ofpackets in the same BSS does not occur during the time period of theCFP, each STA does not require the random back-off time used in the DCF.

The AP and the STA included in the communication system according to thepresent embodiment have the functions of performing a series ofcommunication based on the CSMA/CA described above, but do not need toalways have all the functions.

FIG. 1 is a schematic view illustrating an example of downlink of thecommunication system according to the first embodiment of the invention.In the communication system of FIG. 1, there is an AP 1 and a referencesign 1 a denotes a range (coverage range, Basic service set (BSS)) thatis able to be managed by the AP 1. In the BSS 1 a, there are STAs 2-1 to2-4 connected to the AP 1 and STAs 3-1 to 3-4 that are existing terminalapparatuses (conventional terminal apparatuses, legacy terminalapparatuses). Hereinafter, the STAs 2-1 to 2-4 are simply referred toalso as STAs 2 or first radio receiving apparatuses. Similarly, the STAs3-1 to 3-4 are simply referred to also as STAs 3 or second radioreceiving apparatuses. Compatible standards of the AP 1, the STAs 2, andthe STAs 3 are different from each other. For example, the AP 1 and theSTAs 2 are apparatuses to which the invention is able to be applied andthe STAs 3 are apparatuses to which the invention is not applied. Notethat, the STAs 3 do not need to be always connected to the AP 1 and maybe connected to another AP. Another BSS (Overlapping BSS: OBSS) using atleast a part of frequencies used by the BSS 1 a may exist around the BSS1 a.

The AP 1, the STAs 2, and the STAs 3 perform communication on the basisof the CSMA/CA. Though the present embodiment is intended for aninfrastructure mode in which each of the STAs 2 and the STAs 3 performscommunication with the AP 1, a method of the present embodiment may becarried out also in an ad hoc mode in which STAs directly performcommunication with each other.

In the present embodiment, the AP 1 performs multi-user transmission inwhich packets to the STAs 2-1 to 2-4 are transmitted simultaneously tothe respective STAs 2. Description will be given below by assuming thatthe multi-user transmission is orthogonal frequency division multipleaccess (OFDMA). Note that, the AP 1 may realize the multi-usertransmission by space division multiple access (SDMA) using a pluralityof space resources.

In the BSS 1 a, it is assumed that at least four frequency channels (ch)are able to be used and each of them has a band of 20 MHz. It is assumedthat the AP 1 performs the OFDMA transmission by using the fourchannels. Note that, the AP 1 is also able to perform the OFDMAtransmission by further dividing a channel of 20 MHz into a plurality ofsub-channels and regarding the sub-channels as a plurality of frequencychannels. Note that, the number of channels or sub-channels used for theAP 1 to perform the OFDMA transmission is not limited to four and anynumber of channels may be used. The frequency channels used for the AP 1to perform the OFDMA transmission do not need to be always consecutive.

Hereinafter, what the AP 1 causes each of the STAs 2 to participate inthe OFDMA transmission indicates that the AP 1 is able to transmit asignal frame addressed to the STA 2 by the OFDMA transmission. What theSTA 2 participates in the OFDMA transmission indicates that the STA 2 isable to receive the signal frame that is addressed to the STA 2 andtransmitted from the AP 1 by the OFDMA transmission.

FIG. 2 is a block diagram illustrating an example of a configuration ofthe AP 1 according to the first embodiment of the invention. Asillustrated in FIG. 3, the AP 1 includes a higher layer unit 101, acontrol unit 102, a transmission unit 103, a reception unit 104, and anantenna 105.

The higher layer unit 101 performs processing in a medium access control(MAC) layer and the like. The higher layer unit 101 generatesinformation for performing control of the transmission unit 103 and thereception unit 104 and outputs the information to the control unit 102.The control unit 102 controls the higher layer unit 101, thetransmission unit 103, and the reception unit 104.

The transmission unit 103 further includes a physical channel signalgeneration unit 1031, a frame configuration unit 1032, a control signalgeneration unit 1033, and a radio transmission unit 1034. The physicalchannel signal generation unit 1031 generates baseband signals to betransmitted by the AP 1 to the STAs. The signals generated by thephysical channel signal generation unit 1031 include TFs (Trainingfields) used by the STAs for channel estimation and data transmitted inan MSDU (MAC service data unit). Note that, an example in which thebaseband signals to be transmitted to the STAs 2-1 to 2-4 and the STAs3-1 to 3-4 are generated is indicated because the number of the STAs iseight in FIG. 1, but the present embodiment is not limited thereto.

The frame configuration unit 1032 multiplexes a signal generated by thephysical channel signal generation unit 1031 and a signal generated bythe control signal generation unit 1033, and configures a transmissionframe of the baseband signal actually transmitted by the AP 1.

FIG. 3 is a schematic view illustrating an example of a physical layerof the transmission frame generated by the frame configuration unit 1032according to the present embodiment. The transmission frame includesreference signals such as an L-STF, an L-LTF, a VHT-STF, and a VHT-LTF.The transmission frame also includes control information such as anL-SIG, a VHT-SIG-A, and a VHT-SIG-B. The transmission frame furtherincludes a Data portion. The configuration of the transmission framegenerated by the frame configuration unit 1032 is not limited to FIG. 3and may include other control information (for example, an HT-SIG),reference signals (for example, an HT-LTF), and the like. Thetransmission frame generated by the frame configuration unit 1032 doesnot need to include all the signals such as the L-STF and the VHT-SIG-A.Note that, since information included in the L-SIG or the L-STF isinformation required for the AP 1 or each of the STAs 2 to demodulatethe Data portion, a frame excluding the Data portion will be describedbelow also as a physical layer header (PHY header).

The transmission frame generated by the frame configuration unit 1032 isclassified into some frame types. For example, the frame configurationunit 1032 is able to generate transmission frames of three frame typesof a management frame in which, for example, a connection state betweenapparatuses is managed, a control frame in which a communication statebetween apparatuses is managed, and a data frame including actualtransmission data. The frame configuration unit 1032 is able to includeinformation indicating a frame type to which the transmission frame tobe generated belongs in a medium access control layer header (MACheader) transmitted in the data portion.

The radio transmission unit 1034 performs processing of converting thebaseband signals generated by the frame configuration unit 1032 intoradio frequency (RF) band signals. The processing performed by the radiotransmission unit 1034 includes digital/analog conversion, filtering,frequency conversion from the baseband to the RF band, and the like.

The antenna 105 transmits signals generated by the transmission unit 103to the STAs.

The AP 1 also has a function of receiving signals transmitted from theSTAs. The antenna 105 receives the signals transmitted from the STAs andoutputs the signals to the reception unit 104.

The reception unit 104 includes a physical channel signal demodulationunit 1041 and a radio reception unit 1042. The radio reception unit 1042converts RF band signals input from the antenna 105 to baseband signals.The processing performed by the radio reception unit 1042 includesfrequency conversion from the RF band to the baseband, filtering,analog/digital conversion, and the like. The processing performed by thereception unit 104 may include a function (carrier sense) of measuringperipheral interference in a specific frequency band to reserve thefrequency band.

The physical channel signal demodulation unit 1041 demodulates thebaseband signals output by the radio reception unit 1042. The signalsdemodulated by the physical channel signal demodulation unit 1041 aresignals transmitted in uplink by the STAs 2 and the STAs 3, and have aframe configuration similar to that of the data frame generated by theframe configuration unit 1032. Thus, the physical channel signaldemodulation unit 1041 is able to demodulate the uplink data by the datachannel on the basis of control information transmitted by the controlchannel of the data frame. Further, the physical channel signaldemodulation unit 1041 may include a carrier sense function. Note that,the reception unit 104 may input signal power in the frequency band tothe higher layer unit 101 via the control unit 102 and the higher layerunit 101 may perform processing associated with carrier sense.

FIG. 4 is a flowchart illustrating a flow of signal processing of the AP1 according to the present embodiment. An operation of the AP 1 will bedescribed below with reference to FIGS. 2 and 4.

Before starting OFDMA transmission, the AP 1 is able to notify(broadcast or signal), into the BSS 1 a, function information(capability information) indicating that the AP 1 has a function ofperforming the OFDMA transmission. First, in accordance with thefunction of the AP 1, power consumption of the AP 1, an amount oftraffic to each of the STAs belonging to the BSS 1 a, which isaccumulated in the AP 1, and the like, the higher layer unit 101 of theAP 1 determines whether or not the AP 1 performs the OFDMA transmission(step S401). When not performing the OFDMA transmission (step S401/N),the AP 1 does not perform an operation described below (step S402-2).Note that, the AP 1 may perform an operation based on conventionalCSMA/CA subsequently to step S401/N.

When the AP 1 performs the OFDMA transmission (step S402-1), thetransmission unit 103 then generates, in accordance with thedetermination of the higher layer unit 101, a signal frame fornotifying, into the BSS 1 a, function information (also referred to asfirst function information or OFDMA function information) indicatingthat the AP 1 has the function of performing the OFDMA transmission(step S402). Hereinafter, the signal frame including the functioninformation is referred to as a function information frame (alsoreferred to as a first function information frame or an OFDMA functioninformation frame). For example, the transmission unit 103 is able toinclude, in a beacon frame, a one-bit function information field (alsoreferred to as a first function information field or an OFDMA field)indicating the first function information. For example, when the AP 1has the function of performing the OFDMA transmission, the transmissionunit 103 may generate the beacon frame in which “1” is described in theOFDMA field of the beacon frame. On the other hand, when the AP 1 doesnot have the function of performing the OFDMA transmission or the AP 1does not perform the OFDMA transmission, the transmission unit 103 maygenerate the beacon frame in which “0” is described in the OFDMA fieldof the beacon frame. Similarly, the transmission unit 103 is able toinclude the OFDMA field in another management frame (for example, aprobe response frame).

The AP 1 is able to expect, of each of the STAs 2 in the BSS 1 a,transmission of a function information response frame (details thereofwill be described below) including function response information withrespect to the signal frame including the function informationtransmitted by the AP 1. The transmission unit 103 is able to include,in the beacon frame, a response permitted period field indicating aperiod (response permitted period) during which a response to the OFDMAfield is permitted. In the OFDMA transmission, the AP 1 is able totransmit a data signal only to the STA 2 that has transmitted thefunction information response frame received within the responsepermitted period. Such control makes it possible for the AP 1 to easilyselect the STA 2 that is caused to participate in the OFDMAtransmission.

The transmission unit 103 is also able to describe the first functioninformation in a signal frame other than the beacon frame and themanagement frame such as the probe response frame. For example, thetransmission unit 103 is able to add the function information or theresponse permitted period to an existing control frame, such as a nulldata packet announcement (NDPA) frame, for transmission to the STA 2.The transmission unit 103 may describe an individual address, aplurality of individual addresses, or a group address of each of theSTAs 2 in the signal frame in which the function information isdescribed.

Next, the transmission unit 103 transmits, via the antenna 105, thesignal frame including the function information (step S403). Note that,the transmission unit 103 is able to transmit the signal frame includingthe function information on the basis of the DCF.

Next, the reception unit 104 enters into a reception operation forreceiving a function information response frame (also referred to as afirst function information response frame or an OFDMA functioninformation response frame) that is transmitted by each of the STAs 2 inthe BSS 1 a and includes the function response information (step S404).The reception unit 104 may always or periodically enter into thereception operation after the transmission unit 103 transmits the signalframe including the function information. When a response permittedperiod is included in the signal frame that is transmitted by thetransmission unit 103 and includes the function information, thereception unit 104 may enter into the reception operation only duringthe response permitted period. The reception unit 104 notifies thehigher layer unit 101 of information about the received functioninformation response frame, and the higher layer unit 101 decides, onthe basis of the information about the received function informationresponse frame, the STA 2 that is caused to participate in the OFDMAtransmission (step S405).

The function information response frame includes information indicatingwhether or not the STA 2 that has received the function informationframe is capable of the OFDMA transmission. For example, the functioninformation response frame has a one-bit function capability field (forexample, an OFDMA capability field) indicating whether or not the STA 2is capable of the OFDMA transmission. When “1” is described in thefunction capability field of the function information response frame,the AP 1 is able to cause the STA 2 that has transmitted the functioninformation response frame to participate in the OFDMA transmission. Onthe other hand, when “0” is described in the function capability fieldof the function information response frame, the AP 1 does not cause theSTA 2 that has transmitted the function information response frame toparticipate in the OFDMA transmission.

The function information response frame may also have a one-bit refusefield (for example, an OFDMA refuse field) indicating whether or not theSTA 2 refuses the participation to the OFDMA transmission. When refusingthe participation to the OFDMA transmission, the STA 2 is able todescribe “1” in the refuse field and perform transmission to the AP 1.The AP 1 is able to perform control so that the STA 2 that has performedthe transmission by describing “1” in the refuse field does notparticipate in the OFDMA transmission.

The function information response frame may also have a functionincapability field (for example, an OFDMA incapability field) indicatingthat the STA 2 is incapable of the OFDMA transmission. When the STA 2does not have a function for supporting the OFDMA transmission, the STA2 is able to describe “1” in the function incapability field and performtransmission to the AP 1. The AP 1 is able to perform control so thatthe STA 2 that has performed the transmission by describing “1” in thefunction incapability field does not participate in the OFDMAtransmission.

When the AP 1 transmits a beacon frame or a probe response frame withthe function information included therein, the STA 2 is able to use amanagement frame associated with connection processing, such as anauthentication frame, a connection request frame, or a reconnectionrequest frame, as the function information response frame. For example,the STA 2 is able to include the function capability field in theconnection request frame for transmission to the AP 1. The AP 1 reads avalue of the function capability field of the connection request frametransmitted from the STA 2, and when “1” is described in the functioncapability field, the AP 1 is able to permit connection of the STA 2,and otherwise (that is, when “0” is described in the function capabilityfield), the AP 1 is able to refuse connection of the STA 2.

The AP 1 is also able to transmit a resource reserving frame with thefunction information included therein. Here, the resource reservingframe is a signal frame transmitted by the AP 1 (or the STA 2) in orderfor the AP 1 (or the STA 2) to reserve a radio resource used fortransmission of a predetermined signal frame before transmission of thepredetermined signal frame. In this case, when the STA 2 that hasreceived the resource reserving frame including the function informationis capable of the OFDMA transmission, the STA 2 is able to transmit aresource reserving response frame, such as CTS, in response to theresource reserving frame. On the other hand, the STA 2 that is incapableof the OFDMA transmission or refuses reception of the signal frametransmitted by the OFDMA transmission may not transmit the resourcereserving response frame in response to the resource reserving frame.The AP 1 is able to cause the STA 2 that has transmitted the resourcereserving response frame in response to the resource reserving frameincluding the function information to participate in the OFDMAtransmission.

Note that, the AP 1 is able to generate the resource reserving frameincluding the function information in accordance with a frame format ofan RTS specified by the IEEE802.11 standard. For example, a field (forexample, a receiver address field (RA)) in which information indicatingthe function information is described, and the information indicatingthe function information are able to be shared in advance between the AP1 and the STA 2. For example, when an address of the AP 1 is describedin an RA of an RTS frame, the AP 1 is able to use the RTS frame as aframe indicating the function information.

FIG. 5 is a block diagram illustrating a configuration example of theSTA 2 according to the present embodiment. As illustrated in FIG. 5, theSTA 2 includes a higher layer unit 201, a control unit 202, atransmission unit 203, a reception unit 204, and an antenna 205.

The higher layer unit 201 performs processing of a MAC layer and thelike. The higher layer unit 201 generates information for performingcontrol of the transmission unit 203 and the reception unit 204 andoutputs the information to the control unit 202.

The antenna 205 receives a signal transmitted by the AP 1 and outputsthe signal to the reception unit 204.

The reception unit 204 includes a physical channel signal demodulationunit 2041, a control information monitoring unit 2042, and a radioreception unit 2043. The radio reception unit 2043 converts an RF bandsignal input from the antenna 205 into a baseband signal. The processingperformed by the radio reception unit 2043 includes frequency conversionfrom the RF band to the baseband, filtering, analog/digital conversion,and the like.

The control information monitoring unit 2042 reads information describedin a PHY header (for example, an L-SIG or a VHT-SIG-A) of a transmissionframe transmitted by the AP 1 from the baseband signal output by theradio reception unit 2043 and inputs the information to the physicalchannel signal demodulation unit 2041.

On the basis of the control information acquired by the controlinformation monitoring unit 2042, the physical channel signaldemodulation unit 2041 demodulates the transmission frame transmitted bythe AP 1, and inputs a demodulation result to the higher layer unit 201via the control unit 202.

The higher layer unit 201 interprets data, which is demodulated by thephysical channel signal demodulation unit 2041, in a MAC layer, an LLC(Logical Link Control) layer, and a transport layer. As processing inthe MAC layer of the higher layer unit 201, various information is ableto be acquired from the transmission frame transmitted by the AP 1. Forexample, when the higher layer unit 201 interprets the transmissionframe transmitted by the AP 1 as a beacon frame, it is possible toacquire, for example, information indicating a function (capability) ofthe AP 1 described in the beacon frame.

The processing performed by the reception unit 204 may include afunction (carrier sense) of measuring peripheral interference in aspecific frequency band to reserve the frequency band.

The STA 2 also has a function of transmitting a signal. The antenna 205transmits an RF band signal generated by the transmission unit 203 tothe AP 1.

The transmission unit 203 includes a physical channel signal generationunit 2031, a control signal generation unit 2033, a frame configurationunit 2032, and a radio transmission unit 2034. The physical channelsignal generation unit 2031 generates a baseband signal to betransmitted by the STA 2 to the AP 1. The control signal generation unit2033 generates a control signal used for the AP 1 to demodulate thesignal generated by the physical channel signal generation unit 2031.The frame configuration unit 2032 generates a signal frame, for example,as illustrated in FIG. 9 on the basis of the signals generated by thephysical channel signal generation unit 2031 and the control signalgeneration unit 2032.

The radio transmission unit 2034 converts the baseband signal generatedby the frame configuration unit 2032 into an RF band signal. Theprocessing performed by the radio transmission unit 2034 includesdigital/analog conversion, filtering, frequency conversion from thebaseband to the RF band, and the like.

FIG. 6 is a flowchart for explaining an example of signal processing ofthe STA 2 according to the present embodiment. An operation of the STA 2will be described below with reference to FIGS. 5 and 6.

First, the reception unit 204 receives a function information frametransmitted by the AP 1 and notifies the higher layer unit 201 of ademodulation result thereof (step S601).

The higher layer unit 201 reads content of the description (for example,information of a function information field) in the function informationframe, and determines whether or not the AP 1 has a function ofperforming OFDMA transmission and determines whether or not the STA 2has a function of participating in the OFDMA transmission (step S602).The higher layer unit 201 then generates function response informationindicating whether or not the STA 2 has the function of participating inthe OFDMA transmission.

Next, on the basis of the determination by the higher layer unit 201 atstep S602, the transmission unit 203 generates a function informationresponse frame including the function response information (step S603).When the higher layer unit 201 determines that the STA 2 does not havethe function of participating in the OFDMA transmission, the receptionunit 204 is able to describe, in a function capability field of thefunction information response frame, information indicating that STA 2does not have the function of participating in the OFDMA transmission asthe function response information. On the other hand, when the higherlayer unit 201 determines that the STA 2 has the function ofparticipating in the OFDMA transmission, the reception unit 204 is ableto describe, in the function capability field of the functioninformation response frame, information indicating that the STA 2 hasthe function of participating in the OFDMA transmission. Note that, evenwhen the function information frame transmitted by the AP 1 is notreceived, the STA 2 may transmit the function information response frameincluding the function capability field to the AP 1.

Then, the transmission unit 203 transmits the generated functioninformation response frame (step S604). Note that, the transmission unit203 is able to transmit the generated function information responseframe on the basis of the DCF.

Since the STA 2 is able to describe the function capability field in amanagement frame such as a connection request frame, the STA 2 is ableto decide the AP 1 to be connected, on the basis of description in afunction information field of a beacon frame transmitted by the AP 1.For example, when the STA 2 does not have the function of participatingin the OFDMA transmission or refuses the participation to the OFDMAtransmission, the STA 2 is able to refuse connection (or authentication)to the AP 1 that transmits the beacon frame (or probe response frame)including the function information field indicating that the function ofperforming the OFDMA transmission is included. The STA 2 is also able totransmit a signal frame other than the management frame with thefunction capability field included therein.

The STA 2 is able to include, in the function information responseframe, information indicating whether or not the STA 2 is capable of theOFDMA transmission. For example, the STA 2 is able to include, in thefunction information response frame, a one-bit function capability field(for example, an OFDMA capability field) indicating whether or not theSTA 2 is capable of the OFDMA transmission. When the STA 2 is able toparticipate in the OFDMA transmission, the STA 2 is able to describe “1”in the function capability field in order to indicate that the STA 2 isable to participate in the OFDMA transmission. On the other hand, whenthe STA 2 does not have the function of participating in the OFDMAtransmission or refuses the participation to the OFDMA transmission, theSTA 2 is able to describe “0” in the function capability field in orderto indicate that the STA 2 does not have the function of participatingin the OFDMA transmission or refuses the participation to the OFDMAtransmission.

The STA 2 is also able to include, in the function information responseframe, a one-bit refuse field (for example, an OFDMA refuse field)indicating whether or not the STA 2 refuses the participation to theOFDMA transmission. When the STA 2 refuses the participation to theOFDMA transmission, the STA 2 is able to describe “1” in the refusefield and perform transmission to the AP 1. On the other hand, when theSTA 2 does not refuse the participation to the OFDMA transmission, theSTA 2 is able to describe “0” in the refuse field and performtransmission to the AP 1.

The STA 2 is also able to include, in the function information responseframe, a function incapability field (for example, an OFDMA incapabilityfield) indicating that the STA 2 is incapable of the OFDMA transmission.When the STA 2 does not have the function for supporting the OFDMAtransmission, the STA 2 is able to describe “1” in the functionincapability field and perform transmission to the AP 1. On the otherhand, when the STA 2 has the function for supporting the OFDMAtransmission, the STA 2 is able to describe “0” in the functionincapability field and perform transmission to the AP 1.

According to the communication system including the AP 1 and the STAs 2described above, the OFDMA transmission is realized while suppressingoverhead, thus making it possible to contribute to improvement offrequency efficiency of the communication system.

2. Second Embodiment

The AP 1 and the STAs 2 according to the second embodiment provide acommunication system in which, prior to OFDMA transmission, a radioresource (for example, a frequency channel) between the AP 1 and each ofthe STAs 2 is able to be highly efficiently reserved.

The AP 1 and the STAs 2 according to the present embodiment areconfigured similarly to those of the first embodiment.

The AP 1 according to the present embodiment has a function oftransmitting, into the BSS 1 a, a resource reserving frame for reservinga radio resource between the AP 1 and each of the STAs 2. Note that,similarly to the AP 1 according to the first embodiment, the AP 1according to the present embodiment is able to transmit a functioninformation frame to the STAs 2 before the OFDMA transmission. Thoughthe AP 1 is able to decide, on the basis of function informationresponse frames transmitted from the STAs 2, the STA 2 that is caused toparticipate in the OFDMA transmission, the AP 1 and the STAs 2 accordingto the present embodiment may not necessarily exchange the functioninformation frame and the function information response frame.

The AP 1 is able to transmit an RTS frame into the BSS 1 a as a resourcereserving frame. Note that, though the AP 1 describes an individualaddress in an RA of an RTS frame of the existing IEEE802.11 standard,the AP 1 according to the present embodiment describes, in an RA, agroup address or information that is decided in advance between the AP 1and the STAs 2 and is thus able to transmit resource reserving signalsto a plurality of STAs 2 in the BSS 1 a that may be caused toparticipate in the OFDMA transmission. In the following description, itis assumed that the AP 1 transmits resource reserving frames in allradio resources that may be used for the OFDMA transmission. Here, theradio resource is defined by a frequency (or a frequency channel), atime, a space, a code, and the like. For example, the AP 1 is able totransmit each of the resource reserving frames to a frequency channelfor each 20 MHz, which is used for the OFDMA transmission.

When each of the STAs 2 that has received the resource reserving frametransmitted from the AP 1 interprets the resource reserving frame as aresource reserving frame to the STA 2, the STA 2 is able to transmit aresource reserving response frame to the AP 1. At this time, the STA 2is able to transmit the resource reserving response frame to a radioresource in which the STA 2 does not receive an interference signal,that is, a radio resource that is able to be interpreted as being in anidle state. The STA 2 may transmit the resource reserving response frameto all radio resources that are able to be interpreted as being in theidle state or may transmit the resource reserving response frame only toa part of radio resources.

In this case, the AP 1 according to the present embodiment transmits aresource reserving frame to a plurality of STAs 2 in the BSS 1 a at thesame time. Thus, when the STAs 2 that have received the resourcereserving frame transmit resource reserving response frames at the sametime, the AP 1 is able to understand that a radio resource in which theresource reserving response frames are received is able to be reservedat least in a part of the BSS 1 a. However, the AP 1 is not able todetermine in which range in the BSS 1 a the radio resource is able to bereserved. Here, considered is a case where each of the STAs 2 transmitsthe resource reserving response frame with specific information includedtherein. With such control, while the AP 1 is able to interpret whichSTA 2 has transmitted the resource reserving response frame, each of theSTAs 3 serving as the legacy terminal apparatus is not able to interpretthe resource reserving response frame as the resource reserving responseframe even when having received the resource reserving response frame.Thus, the STA 2 according to the present embodiment generates theresource reserving response frame so that the STA 3 serving as thelegacy terminal apparatus is able to recognize it as the resourcereserving response frame and the AP 1 is able to interpret which STA 2has transmitted the resource reserving response frame.

FIG. 7 is a schematic view illustrating an example of a frame format ofa resource reserving response frame transmitted by the STA 2 accordingto the present embodiment. Here, for simplification of the description,it is assumed that the STA 2-1 and the STA 2-2 in the BSS 1 a transmitresource reserving response frames by the same radio resource, but thepresent embodiment is not limited to such an example. For example, theremay be three or more STAs 2 or the STAs 2 may transmit resourcereserving response frames by a plurality of radio resources.

The transmission unit 203 of the STA 2 according to the presentembodiment generates a resource reserving response frame common withthat of another STA 2. Here, the resource reserving response frameaccording to the present embodiment includes a PHY header, such as asynchronization signal (for example, L-STF), a reference signal (forexample, L-LTF), and a control signal (for example, L-SIG), that is usedfor the AP 1 to demodulate the resource reserving response frame and adata portion (for example, Data) indicating content of the resourcereserving response frame. The Data includes, for example, a MAC headerthat is able to be interpreted by the higher layer unit 101 of the AP 1in a MAC layer. In order for the STA 3 serving as the legacy terminalapparatus to recognize the frame as the resource reserving responseframe, the transmission unit 203 of the STA 2 is able to generate, asthe resource reserving response frame, a CTS frame specified by theexisting IEEE802.11 standard. When the STA 2 transmits the resourcereserving response frame at the same time with another STA 2, the STA 3serving as the legacy terminal apparatus and the AP 1 are not able todetermine which STA 2 has transmitted the resource reserving responseframe as described above. For example, in the case of FIG. 7 as anexample, the AP 1 is not able to determine whether one of the STA 2-1and the STA 2-2 has transmitted the resource reserving response frame orboth of the STA 2-1 and the STA 2-2 have transmitted the resourcereserving response frame.

Thus, the transmission unit 203 of each of the STAs 2 according to thepresent embodiment gives a cyclic shift to the generated resourcereserving response frame. FIG. 8 illustrates an example of a method ofgenerating the resource reserving response frame according to thepresent embodiment. Here, for simplification of the description, it isassumed that the resource reserving response frame is constituted byL-LTF and Data each of which is composed of one OFDM symbol and thenumber of OFDM samples constituting the OFDM symbol is four, and a guardinterval (cyclic prefix) is constituted by two samples. Of course, theresource reserving response frame may include another element (forexample, L-STF) and the number of OFDM symbols constituting the L-STF orthe like and the number of samples constituting the OFDM symbol or theguard interval are not limited thereto.

As describing FIG. 8 as an example, the transmission unit 203 of the STA2-1 does not give the cyclic shift to the resource reserving responseframe. In other words, the transmission unit 203 of the STA 2-1 givesthe cyclic shift of zero sample to the resource reserving responseframe. The transmission unit 203 of the STA 2-2 gives the cyclic shiftof two samples to the resource reserving response frame.

The transmission unit 203 of each of the STAs 2 is able to decide, inthe STA 2, a cyclic shift amount given to the resource reservingresponse frame. For example, the STA 2 is able to decide the cyclicshift amount on the basis of the AID assigned to the STA 2 by the AP 1.In this case, by applying some kind of calculation to the AID (forexample, the STA 2 is able to perform reminder by summing up theassigned AID and dividing a result of the sum by the number of OFDMsamples), the STA is able to decide the cyclic shift amount. Thus, theAP 1 is also able to decide the AID by assuming the cyclic shift amountdecided by the STA 2.

The AP 1 is able to explicitly perform signaling of the cyclic shiftamount to the STAs 2. For example, the AP 1 is able to describe thecyclic shift amount in a connection response frame or an authenticationframe with respect to a connection request from each of the STAs 2 andperform transmission to the STA 2.

The AP 1 is also able to implicitly perform signaling of the cyclicshift amount to the STAs 2. For example, the AP 1 is able to describe agroup ID in the resource reserving frame. Each of the STAs 2 is able tojudge the cyclic shift amount on the basis of an ordinal position atwhich an address of the STA 2 is described in a group specified by thegroup ID. For example, a specific integral value is able to be decidedbetween the AP 1 and each of the STAs 2, so that the STA 2 is able todecide the cyclic shift amount by multiplying the integral value by theorder at which an address of the STA 2 is described in the groupspecified by the group ID.

The STA 2 may change, for each radio resource, a phase rotation amountof phase rotation applied to the resource reserving frame. For example,considered is a case where the STA 2-1 and the STA 2-2 transmit resourcereserving response frames to a predetermined radio resource (alsoreferred to as a first radio resource) by using the cyclic shift amountas illustrated in FIG. 8. At this time, with respect to a resourcereserving response frame transmitted from a radio resource (alsoreferred to as a second radio resource) different from the predeterminedradio resource, the STA 2-2 is able to transmit the resource reservingresponse frame without giving the cyclic shift and the STA 2-1 is ableto transmit the resource reserving response frame by giving the cyclicshift.

The reception unit 104 of the AP 1 receives the resource reservingresponse frames transmitted from the STA 2-1 and the STA 2-2 and thenapplies Discrete Fourier Transform (DFT) (or Fast Fourier Transform:FFT) to OFDM symbols constituting the resource reserving response framesand performs sub-carrier demodulation. In order to demodulate the dataportion, channel estimation is performed by using the L-LTF.

A method of the channel estimation performed by the reception unit 104is not limited, and reverse modulation based on a reference signalsequence used for the L-LTF may be performed, for example. Aconventional AP 1 performs demodulation for the data portion on thebasis of a channel estimation value obtained through the reversemodulation. The reception unit 104 of the AP 1 according to the presentembodiment further applies Inverse Discrete Fourier Transform (IDFT) (orInverse Fast Fourier Transform: IFFT) to the channel estimation value.

FIG. 9 is a schematic view illustrating an example of a state of anInverse Discrete Fourier Transform output applied to a channelestimation value by the reception unit 104 according to the presentembodiment. Since a frequency transfer function (actually, an estimationvalue of the frequency transfer function) of a channel between the AP 1and the STA 2 is obtained when the reception unit 104 applies reversemodulation to the L-LTF, the Discrete Fourier Transform output withrespect to a result of the reverse modulation by the reception unit 104is an instantaneous impulse response (actually, an estimation value ofthe instantaneous impulse response of the channel) of the channelbetween the AP 1 and the STA 2. Hereinafter, for simplification of thedescription, it is assumed that the channel between the AP 1 and the STA2 is a two-path channel model and delay time between paths is onesample. Here, time of one sample is a sampling period of the DFT or theIDFT. Note that, in the present embodiment, it is assumed that a valueobtained by applying the IDFT (or the IFFT) to the frequency transferfunction of the channel between the AP 1 and the STA 2 is aninstantaneous impulse response (or simply a channel impulse response) ofthe channel.

Since the STA 2-1 does not give the cyclic shift to the L-LTF, theinstantaneous impulse response of the channel between the AP 1 and theSTA 2-1 is output at the zeroth sample and the first sample of the IDFToutput of the reception unit 104. On the other hand, since the STA 2-2gives the cyclic shift of two samples to the L-LTF, the instantaneousimpulse response of the channel between the AP 1 and the STA 2-2 isoutput at the second sample and the third sample of the IDFT output ofthe reception unit 104. Thus, by grasping in advance the cyclic shiftamount applied to the resource reserving response frame by each of theSTAs 2, the AP 1 is able to grasp which STA 2 has transmitted theresource reserving response frame on the basis of the IDFT output of thereception unit 104.

As describing FIG. 9 as an example, when the instantaneous impulseresponse is observed at the zeroth sample and the first sample of theIDFT output of the reception unit 104, the AP 1 is able to understandthat the STA 2-1 has transmitted the resource reserving response frame.When the instantaneous impulse response is observed at the second sampleand the third sample of the IDFT output of the reception unit 104, theAP 1 is able to understand that the STA 2-2 has transmitted the resourcereserving response frame. When the STAs 2 generate the same resourcereserving response frames and apply different cyclic shifts to theresource reserving response frames as described above, the AP 1 is ableto grasp which STA 2 has transmitted the resource reserving responseframe.

Note that, the reception unit 104 of the AP 1 is not always required toapply IDFT processing to the resource reserving response frame to whichthe cyclic shift is given. When each of the STAs 2 applies the cyclicshift to a predetermined resource reserving response frame, a frequencyresponse (that is, a DFT output with respect to the resource reservingresponse frame) of the resource reserving response frame is obtained byapplying phase rotation corresponding to the cyclic shift to a frequencyresponse of the resource reserving response frame to which the cyclicshift is not given. For example, when a DFT output of an OFDM signalincluded in the resource reserving response frame to which the cyclicshift is not given is {S(k); k=0 to (N_(c)−1)} (N_(c) is a DFT pointnumber), a DFT output of an OFDM signal included in the resourcereserving response frame to which the cyclic shift of an M sample isgiven is {S(k)exp(j2πMk/Nc; k=0 to (N_(c)−1)}. Thus, by calculating acorrelation between the DFT output of the resource reserving responseframe transmitted by each of the STAs 2 and the DFT output of the OFDMsignal included in the resource reserving response frame to which phaserotation is applied by the cyclic shift amount that is defined inadvance between the AP 1 and each of the STAs 2, the reception portion104 of the AP 1 is able to determine which STA 2 has transmitted theresource reserving response frame. For example, in a case where thereception portion 104 calculates a correlation between a DFT output ofan OFDM signal included in the resource reserving response frame towhich a cyclic shift of an M sample is given and a DFT output of an OFDMsignal included in a received resource reserving response frame, when acorrelation output value thus obtained is greater than a predeterminedvalue (threshold), the reception unit 104 is able to determine that theSTA 2 that gives the cyclic shift of the M sample to the resourcereserving response frame has transmitted the received resource reservingresponse frame.

Note that, the cyclic shift amount given by each of the STAs 2 to aresource reserving response frame is not limited. For example, the STA 2(or the AP 1) may use a random integer from 1 to N as the cyclic shiftamount with the number N of samples of an OFDM signal included in theresource reserving response frame as an upper limit. The STA 2 (or theAP 1) may use a random integer from 1 to N_(g) as the cyclic shiftamount with the number N_(g) of samples of a guard interval (or a cyclicprefix) of an OFDM signal included in the resource reserving responseframe as an upper limit.

Note that, description has been given by taking a case where the AP 1transmits a signal frame to a plurality of STAs 2 by OFDMA transmissionas an example. A method according to the present embodiment is alsoapplicable to a case where a plurality of STAs 2 transmit signal framesto the AP 1 by OFDMA transmission. In this case, as described above, itis possible that the AP 1 transmits a resource reserving frame to theplurality of STAs 2 and the STAs 2 transmit resource reserving responseframes corresponding to the resource reserving frame at the same time.It is also possible that the plurality of STAs 2 apply the specificcyclic shift to predetermined resource reserving frames and thentransmit the resource reserving frames at the same time. With the methoddescribed above, the AP 1 having received the resource reserving framesis able to discriminate the STAs 2 that have transmitted the resourcereserving frames. Thus, when the AP 1 receives the resource reservingframes and determines that a radio resource in which the resourcereserving frames have been transmitted is in an idle state, the AP 1 isable to transmit a common resource reserving response frame by using theradio resource that is determined to be in the idle state. The AP 1 maytransmit an individual resource reserving response frame to the STAs 2to which the radio resource that is determined to be in the idle stateis assigned.

According to the AP 1 and the plurality of STAs 2 described above, theplurality of STAs 2 are able to transmit resource reserving responseframes at the same time. The STA 3 serving as the legacy terminalapparatus is able to correctly receive the resource reserving responseframes transmitted by the plurality of STAs 2 at the same time. Bygrasping in advance a cyclic shift amount applied to the resourcereserving response frames by the STAs 2, the AP 1 is able to correctlydetermine which STAs 2 have transmitted the resource reserving responseframes. Thus, according to the AP 1 and the STAs 2, the AP 1 is able toefficiently reserve a radio resource used for OFDMA transmission whilesuppressing overhead associated with transmission of a resourcereserving frame and a resource reserving response frame, and further,the AP 1 is able to correctly discriminate the STA 2 that hastransmitted the resource reserving response frame, resulting inimprovement of user throughput of the STAs 2.

3. Common in All Embodiments

Note that, a program which runs in the AP 1, the STAs 2, and the STAs 3according to the invention is a program that controls a CPU and the like(program that causes a computer to function) such that the functions inthe aforementioned embodiments concerning the invention are realized.The pieces of information handled by the apparatuses are temporarilyaccumulated in a RAM during the processing thereof, and then stored invarious ROMs and HDDs and read, corrected, and written by the CPU whennecessary. A recording medium that stores the program therein may be anyof a semiconductor medium (for example, a ROM, a nonvolatile memory cardor the like), an optical recording medium (for example, a DVD, an MO, anMD, a CD, a BD or the like), a magnetic recording medium (for example, amagnetic tape, a flexible disc or the like), and the like. Moreover,there is also a case where, by executing the loaded program, not onlythe functions of the aforementioned embodiments are realized, but alsoby performing processing in cooperation with an operating system, otherapplication programs or the like on the basis of an instruction of theprogram, the functions of the invention may be realized.

When being distributed in the market, the program is able to be storedin a portable recording medium and distributed or be transferred to aserver computer connected through a network such as the Internet. Inthis case, a storage apparatus of the server computer is also includedin the invention. A part or all of the AP 1, the STAs 2, and the STAs 3in the aforementioned embodiments may be realized as an LSI which is atypical integrated circuit. Each functional block of the AP 1, the STAs2, and the STAs 3 may be individually formed into a chip, or a part orall thereof may be integrated and formed into a chip. When eachfunctional block is made into an integrated circuit, an integratedcircuit control unit for controlling them is added.

Further, a method for making into an integrated circuit is not limitedto the LSI and a dedicated circuit or a versatile processor may be usedfor realization. Further, in a case where a technique for making into anintegrated circuit in place of the LSI appears with advance of asemiconductor technique, an integrated circuit by the technique is alsoable to be used.

Note that, the invention of the present application is not limited tothe aforementioned embodiments. The AP 1, the STAs 2, and the STAs 3 ofthe present application are not limited to be applied to a mobilestation apparatus, but, needless to say, are applicable to stationary orunmovable electronic equipment which is installed indoors or outdoorssuch as, for example, AV equipment, kitchen equipment, cleaning/washingmachine, air conditioning equipment, office equipment, automatic vendingmachine, other domestic equipment, and the like.

As above, the embodiments of the invention have been described in detailwith reference to drawings, but specific configurations are not limitedto the embodiments, and a design and the like which are not departedfrom the main subject of the invention are also included in the scope ofclaims.

INDUSTRIAL APPLICABILITY

The invention is suitably used for a radio transmission apparatus, aradio receiving apparatus, a communication system, and a communicationmethod.

Note that, the present international application claims priority fromJapanese Patent Application No. 2015-047811 filed on Mar. 11, 2015, andthe entire contents of Japanese Patent Application No. 2015-047811 arehereby incorporated herein by reference.

REFERENCE SIGNS LIST

1 AP

2, 2-1, 2-2, 2-3, 2-4, 3, 3-1, 3-2, 3-3, 3-4 STA

101, 201 higher layer unit

102, 202 control unit

103, 203 transmission unit

104, 204 reception unit

105, 205 antenna

1031, 2031 physical channel signal generation unit

1032, 2032 frame configuration unit

1033, 2033 control signal generation unit

1034, 2034 radio transmission unit

1041, 2041 physical channel signal demodulation unit

1042, 2043 radio reception unit

2042 control information monitoring unit

1. A radio receiving apparatus performing communication with a radiotransmission apparatus that performs multi-user transmission with aplurality of radio receiving apparatuses, the radio receiving apparatuscomprising: a transmission circuit that transmits a frame includingrefuse filed associated with the multi-user transmission when refusingthe participating in the multi-user transmission, “1” is set in therefuse field; and when not refusing the participating in the multi-usertransmission, “0” is set in the refuse field, and a reception circuitthat acquires information indicating whether or not the radiotransmission apparatus enables receiving of the refuse fieldinformation, from a beacon frame transmitted by the radio transmissionapparatus, the frame including refuse filed includes a training filed.2. A radio transmission apparatus that performs multi-user transmissionwith a plurality of radio receiving apparatuses, the radio transmissionapparatus comprising: a reception circuit that receives a frameincluding refuse filed associated with the multi-user transmission fromthe radio receiving apparatus, wherein a transmission circuit thattransmits a beacon frame including information indicating whether or notthe radio transmission apparatus enables accepting of the refuse fieldinformation, wherein the frame including refuse filed includes atraining filed.
 3. A communication method of a radio receiving apparatusperforming communication with a radio transmission apparatus thatperforms multi-user transmission with a plurality of radio receivingapparatuses, the method comprising the steps of: transmitting a frameincluding refuse filed associated with the multi-user transmission whenrefusing the participating in the multi-user transmission, “1” is set inthe refuse field; and when not refusing the participating in themulti-user transmission, “0” is set in the refuse field, and acquiringinformation indicating whether or not the radio transmission apparatusenables receiving of the refuse field information, from a beacon frametransmitted by the radio transmission apparatus, wherein the frameincluding refuse filed includes the training filed.